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However, as well as providing
the route for nutrients into the
unborn child’s body, the
placenta also provides a path
for some harmful agents to
enter the body of the developing child.
Here are a few examples:
Life Issues Institute
We’ve seen that the placenta is
a vital organ for the growing
baby. It allows the transfer of
food and oxygen from the
mother’s bloodstream and
removes waste products e.g.
carbon dioxide from the unborn
child’s.
Rubella virus – The virus that causes the relatively minor condition
Human Sperm / Science Photo Library
This is how your life began.
Fertilisation involves the fusing of
the cell nucleus from the father’s
sperm with the cell nucleus from
the mother’s egg. The male and
female cell nuclei contain genetic
material from the mother and the
father, but the newly fertilised egg
combines this genetic material in a
unique way. A new human life has
begun and is brought into being by
the combination of the sperm and
the egg produced by his or her
parents. The combined genetic
material is different from that of the
father or mother and this new
human’s sex, skin, hair and eye colour are determined at this
point. The way in which the genetic material from the sperm and
egg combine, will also influence many factors later in life e.g.
height, intelligence.
known as Rubella or German measles in children and adults is much
more damaging to the unborn child. If a woman catches rubella during
pregnancy, she will display the same relatively mild symptoms as a
woman who is not pregnant. However, the virus crosses the placenta
into the body of the developing child. If this occurs when the unborn
child’s organs are still developing (i.e. in the first 3 months) then
a condition known as Congenital Rubella Syndrome usually results
which often leads to miscarriage and stillbirths or to birth defects
including congenital heart diseases, cataracts, deafness, and mental
retardation. This was why, in the past, girls in secondary school
received rubella vaccination while boys did not. Now rubella
vaccination is routinely offered to both boys and girls as young
babies/toddlers.
REPRODUCTION
Placenta – not always a lifeline?
Human egg with corona radiata cells / Science Photo Library
How human life begins •
How humans grow before birth
and how damage can occur •
Birth
Alcohol – The damage that alcohol can cause to unborn children has
only been recognised in the past 30 years. There is still a lot that is
not understood but mothers who drink heavily during pregnancy risk
their child suffering from reduced physical growth and learning
disabilities throughout life. The condition is known as fetal alcohol
syndrome. The most recent advice issued in May 2007 is that mothers
should not drink alcohol at all during pregnancy.
Tobacco – When someone smokes a cigarette, a poisonous gas
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Design a poster for display in doctors’ surgeries warning about the
dangers of drinking alcohol while pregnant. You might want to carry
out an internet search engine request on fetal alcohol syndrome to
help you find additional information.
Fro m
Sperm fertilising egg / Science Photo Library
Task:
Cover: 14 week old embryo / Life Issues Institute
called carbon monoxide gets into your bloodstream and cuts down
the oxygen reaching the unborn child. Mothers who smoke during
pregnancy risk giving birth to a baby with a lower birth weight than
average and a higher chance of cot death. The baby may also develop
breathing problems and asthma as they grow older.
Righ
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FERTILISATION
– When human life begins
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Days 6-12 Implantation: Following fertilisation the single cell
divides rapidly time and time again into first, 2, then 4 then 8 cells and
so on. This starts the process of differentiation, where the cells organise
themselves according to their different functions. The journey along the
oviduct to the uterus takes about 4 or 5 days by which time the lining of
the uterus has become soft and spongy in preparation for implantation.
Having reached the uterus the embryo comes into contact with the
uterine lining and over the course of the next six days burrows into it
and by day 12 is completely buried within it.
Life begins for each human being at fertilisation when one of the father’s
sperm penetrates or enters the mother’s egg. The human male and
female reproductive systems are shown below. The testes produce millions
of sperm but the ovaries almost always release only a single egg each
month. After its release from the ovary the egg enters the oviduct.
Sperm enter the vagina during sexual intercourse and begin their upward
journey through the female reproductive tract. A small number of sperm
eventually reach the oviduct where fertilisation occurs.
Photos 1– 4 Life Issues Institute
Life begins at fertilisation
Second month: The embryo grows
8-fold in just 4 weeks (from 5mm at
4 weeks to 40mm at 8 weeks)! At the
end of the sixth week the embryo
has the body form of a human infant.
By the end of the eighth week fingers
and toes are clearly visible as are
the eyes and external ears. This little
girl has her own fingerprints, unique
to her and destined to be used to
identify her once she is born. The
brain develops rapidly during this
period and electrical activity can be
recorded.
Day 28: This baby girl’s body
Bladder
Penis
Urethra
Epididymis
(in this photo 8 weeks after
fertilisation), now completely
embedded within the lining of her
mother’s uterus, lies within a fluid
filled cavity the amniotic sac, which
is formed (or enclosed) by the
amnion, an embryonic membrane.
The implanted embryo, in contact
with the deepest portion of the
uterine lining, forms the placenta,
a vital organ for the growing baby.
The embryo is attached to the
placenta by the developing
umbilical cord, which encloses the
embryo’s major blood vessels.
The mother’s blood flows through
the placenta and is separated from
the blood of the unborn infant by a
thin membrane, which provides
a large surface area for the transfer
of nutrients and gaseous exchange.
The mother’s blood delivers oxygen
and nutrients to the unborn girl’s
blood and removes carbon dioxide
and waste products from her.
Scrotum
Uterus (Womb)
Life Issues Institute
Anatomical drawings ©Annabel Milne 2007
Ovary
Bladder
Cervix
Urethra
Vagina
State of Ohio
Questions:
Look at the photograph of the sperm and egg.
Why do you think sperm have tails?
The woman’s egg is a large cell with a big food reserve.
Why do you think this is?
In humans, like all mammals, fertilisation is internal, that is it takes
place inside the body. Compare this with other animals e.g. frogs
where fertilisation is external i.e. outside the body.
Why do you think frogs fertilise hundreds of eggs?
Why do you think the human ovary releases only one egg each
month?
the developing baby girl reacts to
stimuli with observable responses:
smiling, wrinkling her forehead and
bending her fingers around an object
in the palm of her hand. Reactions to
painful stimuli suggest that at this
stage the infant actually feels pain.
The amniotic sac - baby’s own
capsule: The developing embryo
Testis
Oviduct
Third month: During this period
Questions:
What function do you think the amniotic sac and fluid have?
How is this linked to the fact that fertilisation is internal and usually
results in the birth of only one infant?
Fourth and fifth months:
During this period the ear is
sufficiently well developed for the
infant to respond to a wide variety of
sounds. This unborn girl in the womb
is able to recognise her mother’s
voice.
Fifth month to birth: In the
final months of pregnancy the infant
continues to grow and gain weight,
will wake and sleep in parallel with
her mother and be sensitive to her
moods and emotions.
Science Photo Library
Prostrate gland
Science Photo Library
Vas deferens
is beginning to develop. The head
and trunk appear and the heart is
already beating. This began on
day 21 and will continue until
death perhaps 90 or more years
in the future.
Birth: Birth is a major event for
this newborn girl. Her environment
changes and she will no longer use
her placenta, as she now receives
oxygen through her lungs and food
through her mouth. Although a
significant event, birth is simply a
stage in the child’s life, which began
at fertilisation.